Design patterns are general reusable solutions to common software design problems. They help you write code that is more maintainable, flexible, reusable and scalable
Design patterns are typically divided into three categories:
Creational patterns focus on object creation mechanisms, providing ways to instantiate objects in a flexible manner. Some commonly used creational patterns are:
- Singleton: Ensures a class has only one instance and provides a global point of access to that instance
- Factory Method: Defines an interface for creating objects, but allows subclasses to decide which class to instantiate
- Builder: Separates the construction of a complex object from its representation, allowing the same construction process to create different representations
Structural patterns focus on object composition and typically identify simple ways to realize relationships between different objects. Some commonly used structural patterns are:
- Adapter: Allows the interface of an existing class to be used as another interface. It is often used to make existing classes work with others without modifying their source code
- Decorator: Allows behavior to be added to an object statically or dynamically, without affecting the behavior of other objects from the same class
- Facade: Provides a simplified interface to a complex subsystem, making it easier to use
Behavioral patterns focus on communication between objects and the distribution of responsibilities. Some commonly used behavioral patterns are:
- Observer: Defines a one-to-many dependency between objects, so that when one object changes state, all its dependents are notified and updated automatically
- Strategy: Defines a family of interchangeable algorithms, allowing the algorithm to be selected at runtime
- Template Method: Defines the structure of an algorithm but lets subclasses override specific steps
- Null Object: Provides an object as a surrogate for the lack of an object of a given type